Can you measure the impact of a customer receiving a web application error? If you receive an error yourself, do you contact the site administrator or do you look elsewhere? Personally, I hit refresh, just the once, and then I head back to google.
In a time where 'instant gratification' reigns, can we afford to allow technical errors, however severe or temporary, to meet the eyes of our valued customers? Granted, not all outages are predictable or avoidable but most can be handled elegantly.
The two most common web application errors are "404 - Object Not Found" and "503 Gateway Timeout" and to an administrator, these errors have meaning.
A "404 - Object Not Found" suggests a web admin should start looking at the web servers for a bad link or something that wasn't copied during the last update. A "503 gateway timeout" points towards the application servers, a.k.a. the middle tier. Maybe the App Servers are over utilised? Maybe a congestion issue when trying to reach the database?
We could debate for hours the many diagnostic techniques and the most effective order of steps to resolve the problem but, your customers, the consumers of your service, they don't care.
Back in 5
Forgetting technology for a moment (gasp), how differently would you react to a corner store displaying a "back in 5 minutes" sign versus a locked door with no sign at all? The former acknowledging a temporary disruption in service but promising business as usual in the very near future. The latter being dangerously open to interpretation. Closed all day? Robbery in progress? Liquidation? Where is the incentive for the customer to return either in the near future or ever?
Improvise, Adapt & Overcome
Things don't always go to plan. We see this in the Special Forces with many units adopting the mantra 'Improvise, Adapt and Overcome'. This applies perfectly to Application Delivery. An intelligent services platform that see's the error, alters its response to something aligned with the company image and overcomes the potential loss of business.
There are no excuses for the ugly regurgitations presented by apps and operating systems. To see how your site handles this problem, to force a "404 - Object not found", simply request something you know to be missing. For example: http://www.domainname.com/invalid.html In some cases the response is quite amusing...
 Harvard Economics - Instantaneous Gratification by Christopher Harris and David Laibson